The invention relates to safety switches for machine tools and their analogues. It relates, more particularly, to safety switches employing a weight-sensitive mat with integral switching elements in the machine control circuit.
The art of providing safety switches for machine tools and other potentially dangerous devices is old. Many devices have been proposed in which the operator is required to use both hands to activate the machine process, or in which the presence of the operator, a part of his body, in a given position triggers a light beam/photocell device to prevent machine operation, and so on. All of these safety devices are concerned with two primary causes of industrial accidents, the entrapment of the operator in the machine, and the use of the machine by those unskilled in the safe use thereof, and attempt to prevent the former contingency arising by providing some physical barrier or alarm system between the operator and the danger points on the machine, and the latter by requiring the use of keys or specific operating sequences or codes to cause the machine to perform its operating cycle.
These devices of the prior art are not generally applicable to machine tools in which the machine process is continuous and danger commonly arises not from the process itself but from some extraneous condition, such as the entanglement of the operator's clothing in the workpiece or tool, against which precautions cannot be readily taken. Commonly such machines as drill presses, milling machines, lathes, etc., are not provided with any safety device other than the start/stop switch, and rely on the agility and skill of the operator to press the stop switch before the accident sequence has reached a danger point, a very low level of protection for the operator.
It is, therefore, a primary object of the invention to provide a safety switch for the operator of a machine tool, or its like, incorporating a load-sensitive mat with electrical switching elements, which may be used to terminate machine operation without the use of his hands.
It is also an object of the invention to provide such a safety switch, and associated electrical circuitry, which is readily adapted to conventional machine tool control systems and requires no modification of the basic machine tool.
It is yet another object of the invention to provide a safety device for machine tools which is simple in construction, failsafe in operation, and convenient in use.
It is also the object of the invention to provide quick disconnect means for a mat safety switch as described hereinabove, whereby the removal of the safety switch from the machine circuit will cause the latter to be disabled and inoperative.